Contrast-agent-assisted tomography scans are now an indispensible part of medical imaging technology. Around 80% of all computed tomography examinations (and also a considerable proportion of magnetic resonance tomography examinations) are currently carried out in this way using contrast agents. This means that in addition to the parameter value settings of the respective image recording system other important parameter values for administering the respective contrast agent must be set correctly in order to achieve a sufficient image quality of the captured tomography image data. Medical technology imaging systems or tomography systems principally include all automatic or semi-automatic image recording systems such as ultrasound, computed tomography systems (CT), magnetic resonance tomography systems (MR) and special tomography systems which are designed specifically for contrast-agent-based tomography recordings—for instance SPECT (Single Photon Emission Computed Tomography) or PET (Positron Emission Tomography).
Contrast agents are generally defined as those agents which improve the depiction of structures and functions of the body in imaging procedures such as X-ray diagnostics, magnetic resonance tomography (MRT) and sonography (ultrasound). The effect of contrast agents is to modify the signal which is registered in the respective examination. The purpose of using them is to obtain additional information during the examination. For example, in radiography frequent use is made of contrast agents which absorb the X-rays more strongly than normal soft tissue. Usually no blood vessels are visible on an X-ray image. If for example a solution containing iodine is injected as a contrast agent, the vessels which the solution reaches throw X-ray shadows and in this way become visible. Normally contrast agents are differentiated from so-called tracers. These relate to an artificial, often radioactively marked substance which is internal or external to the body, and which after introduction into the living body participates in the metabolic process and in addition permits or facilitates a wide variety of examinations. In the context of the present application agents conventionally defined as contrast agents as well as tracers are both referred to generally as “contrast agents”.
Contrast agents can be administered in pure form or mixed with other, thinning agents. Thus it is for example usual to admix a dose of a particular contrast agent with a particular quantity of saline solution or to administer these two agents simultaneously.
In medical technology imaging an accumulation of contrast agent in the examination object (normally therefore a patient) which is both sufficient in quantity and also evenly distributed is necessary, in order subsequently on the basis of the captured recording results data to provide a basis for a diagnosis by a physician. Also, to be able to evaluate the recording results data in a so-called postprocessing application, in other words an automatic evaluation device, a particular image quality must be achieved, since otherwise the necessary algorithms, for example during segmentation in postprocessing, supply false or inadequate results.
The reasons for insufficient contrast may be many and varied. For example they include:                Incorrect timing of the imaging scanner after an injection of contrast agent, for example in stenoses: for example in an intravenous injection of a contrast agent the distribution of the contrast agent in the vascular system may be delayed by a vascular stenosis, in other words a narrowing, for instance in the carotid artery, so that for example sufficient contrast agent has not yet arrived in the brain, although this could have been reckoned with.        Scanning does not last long enough, as may occur for example in so-called flash scans. Flash scan means a tomography scan which is performed very quickly, in particular with a fast feed of the patient table.        An inadvertent injection of pure saline solution instead of the contrast agent or a saline/contrast agent mixture.        An erroneous setting of contrast agent parameters, for example in respect of the flow and/or volume of the contrast agent. The contrast agent parameters are often established beforehand in an injection protocol which controls automatic administration of contrast agent. In this, for example, the flow of contrast agent in ml/s and/or the total volume of the contrast agent to be administered is stipulated, as well as (indirectly conditioned by these two parameters) the time which is provided for the administration of contrast agent. Additionally a maximum pressure limit of the injection pressure can be specified as well as numerous other parameter values. After defining all relevant parameter values the contrast agent administration system executes the administration of contrast agent automatically in line with the injection protocol—therefore if unsuitable parameter values are already set in the injection protocol for the scheduled tomography scan, this has an indirect impact on the resulting image quality of the image data resulting from the tomography scan.        An erroneous positioning of the needle, for example a paravasate positioning, in which the target veins are not correctly hit during an injection, so that little or no contrast agent arrives in the veins.        
FIG. 1 shows a sectional image of a human thorax from a contrast-agent-assisted CT scan, in which too much contrast agent has accumulated, whereas FIG. 2 shows a sectional image of the same thorax when sufficient contrast agent has accumulated. It is apparent in FIG. 1 that when too much contrast agent has accumulated the individual organs are displayed with indistinct boundaries, so it is not possible to delineate them sufficiently clearly. In contrast, this delineation is readily possible on the basis of the illustration in FIG. 2.
FIG. 3 shows a sectional image of a thorax from a contrast-agent-assisted CT scan, in which the accumulation of contrast agent in the target structure is insufficient. The result is that at best the spinal column of the patient is dimly identifiable. This sectional image is practically worthless for a diagnosis.
The images from the contrast-agent-assisted scanning procedure are at present either not checked at all or only on the basis of a purely visual inspection of so-called real-time display data or real-time display images. In the context of this application the following basic distinction between image data is made:                Raw image data is data which arises directly during the capture. It hence comprises a collection of detector signals which have not as yet been preprocessed for an image display.        Reconstructed image data is image data which has been derived from the raw image data after a full image reconstruction. It forms the basis for a subsequent diagnosis by medical specialists.        Real-time display data is image data which results from a rough conversion of the raw image data into images and hence in practice can be generated in parallel to the image capture. Real-time display data has a considerably poorer image quality, in particular resolution and quantity of information, than the reconstructed image data according to the above definition. The real-time display data is in particular mostly unfiltered, so that in an extreme case it has strong noise effects as a result of artifacts, etc. It therefore only gives a very simple overview for personnel in situ at the tomography system.        Recording results data is only the raw image data and/or the real-time display data, but not the reconstructed image data. Thus it always involves image data from which a user can draw conclusions about the actual image quality of the image data only with difficulty, if at all.        
For a first quality check only the real-time display data is used in the best case and image displays derived therefrom are evaluated roughly by visual inspection. However, an operator can in this case generally only inadequately assess whether a sufficient contrast has been achieved in the image data; in addition there is usually not enough time for a more thorough check. The actual comprehensive reconstruction of the image data usually takes place in the meantime in the background or subsequent to the tomography scan, so that the reconstructed image data is not available until much later. Hence the actual meaningful quality check of the image data does not currently take place until the diagnosis by a diagnostic physician or when using postprocessing applications.
If ultimately the quality of the recording results data was insufficient, this normally means that a diagnosis or an evaluation is not possible with a postprocessing application, or not to the desired extent, since clinically relevant target structures, for instance vessels, are not available in sufficient quality for a diagnosis. These shortcomings are normally not established until a patient, generally speaking an examination object, is no longer present in the immediate vicinity of the tomography system, but for example has already left the radiology department in question. This results in increased extra work in both organizational and financial terms, possibly delays in further diagnosis and not least in an increased radiation dose, if a complete examination has to be repeated completely at a later time.